I have at least 3 books on my Kindle in each of which the font is specified by the book, i.e., the the user has lost control of the presentation of the text.
See, in a physical book, someone (a worker, a craftsman, an artist) makes the presentation choices for the reader because there’s a physical product that has to be delivered. But in an ebook — and I mean a book of words: zero or few graphics (other than the cover); zero or few simple, narrow tables — the only point is the words. Almost all books are filled with plain, Roman text, with the occasional italics or boldface in the running text. (Chapter and section headings don’t count in this discussion).
If you’re publishing a book of plain text, please, I beg you, leave the font to the reader’s discretion: the face, the size, the line spacing. These give the reader the ability to adjust the comfort level and get to the words.